1. Field of the Invention
The present invention relates to a picture tilt complement circuit for complementing for a tilt of a picture displayed on a screen in a display device, such as a monitor or television receiver, using the Braun tube, such as a color picture tube (CPT) or cathode ray tube (CRT), as an image display.
2. Discussion of Related Art
Usually, a display device, such as a CRT, forms an image using an electron beam focussed on a fluorescent screen. A circuit changing the direction of the electron beam is called a deflecting circuit. There are two kinds of deflecting methods in a deflecting circuit: an electrostatic deflection using electric field; and an electromagnetic deflection using magnetic field. In a television using the electromagnetic deflection, image is formed by applying current of a sawtooth waveform to horizontal and vertical coils.
As one of the display devices which convert signals transmitted from a computer into image to display for a user, a monitor is a representative peripheral device in the computer. The basic configuration of the inner circuit in the monitor will consists of a video card installed inside a computer for providing color signals (R, G, B) and horizontal and vertical sync signals (H.sub.-- Sync and V.sub.-- Sync) necessary for forming an image, a microcomputer for generating a control signal to control an image in a monitor after receiving the horizontal and vertical sync signals from video card, horizontal and vertical deflecting circuits for receiving the horizontal and vertical sync signals and sequentially deflecting an electron beam formed in an electron gun in the CRT from top to bottom and from left to right using a deflection yoke so as to form a picture like a photograph, a high voltage circuit for supplying high voltage to an anode in the CRT using a retrace pulse produced from an output port of the horizontal deflecting circuit based on the principle of a switching circuit and technology relating to high voltage, a video pre-amplifier for maintaining a specified level of voltage after amplifying the low video signals transmitted from the video card using a low voltage amplifier, and video main amplifier for supplying energy to each pixel displayed on the CRT after re-amplifying the video signals amplified by video pre-amplifier.
The electron gun forms an electron beam according to the video signals. The deflection circuit horizontally and vertically deflects the electron beam and scans it on the fluorescent screen in front, thus representing a specified picture. The electron beam is deflected using magnetic field. The horizontal and vertical deflecting coils installed in a funnel portion in the Braun tube generate horizontal and vertical deflection magnetic fields, respectively, and deflect the electron beam.
The earth has its proper magnetic field called as an earth magnetic field. This earth magnetic field influences deflection of electron beam by the horizontal and vertical deflecting coils, thus the picture is displayed on the screen in a monitor on the tilt to left or right, not horizontally.
Horizontal and vertical deflecting coils are utilized to complement for the tilt of the picture displayed through a Braun tube in prior art by creating a complementing magnetic field. This complementing magnetic field moves the tilt of the picture on the screen counterclockwise, and the degree of tilt complement is variable.
As described above, the tilt of the picture on a screen is complemented in such a manner to of varying a complementing magnetic field by controlling the direction and the amount of current across a complementing coil. However, the magnetic field created by the complementing coil often has a bad impact on the quality of picture. A Braun tube is usually much influenced by an ambient magnetic field. Because of the ambient magnetic field, an electron beam, which is scanned on a screen, drifts, thus convergence is varied as well as there occurs blur on the screen. Much current must be applied to the complementing coil to make the complementing coil create a complementing magnetic field, thereby consuming much electric power and generating much heat causing reduction of life of parts. Additionally, the prior art involves a problem that a special complement coil is required.